The Clinical Sequence of Physiological Effects of Ionizing Radiation in Animals

Abstract

Ionizing radiations constitute a useful therapeutic and experimental tool but, at the same time, a dangerous one. The increase in availability of sources of radiation with modern advancements in the field of nuclear energy makes possible the inadvertent exposure of many more people than was ever possible when x-ray tubes and radium constituted the principal known sources of radiation. In the event of an atomic war, entire populations will be subjected to radiation hazards. Radioactive materials deposited in the bodies of workers in the atomic energy industry may cause many disabilities. It is increasingly important, therefore, that the clinical effects of radiation be understood and methods of therapy be explored and made available. Researches in clinical physiology and biochemistry at the Metallurgical Laboratory have been concerned with (1) ascertaining whether different kinds of ionizing radiation have similar effects upon the mammalian body; (2) measuring sensitive reactions as a function of dose, in the hope of setting permissible exposure limits; (3) searching for sensitive biological indicators of exposure; (4) describing the course of radiation damage sufficiently to suggest profitable directions for research into mechanisms of such damage that might eventually lead to effective therapy. None of these objectives has been attained in a final form, but sufficient data are available to justify a summary at this time. Extensive reviews of the pre-war experimental literature on the effects of x-radiation upon animals have been published by Dunlap and Friedman in Shields Warren's monograph (1942–43) on the Pathology of Radiation. The emphasis in the present paper is upon work done in the Health Division of the Metallurgical Laboratory. The collaboration of numerous persons has made possible a wide variety of physiological and biochemical measurements on individual animals. Contributions by the following persons should be acknowledged: E. E. Painter, M. N. Swift, and Owen France, physiologists; Austin M. Brues, Samuel Schwartz, and Margaret Rand, biochemists; Leon o. Jacobson, hematologist; Hermann Lisco, pathologist; J. G. Allen and Donald Buchanan, clinicians; G. Sacher, statistician; and numerous technicians who have carried out much of the detail of the experiments. The general pattern of the clinical effects of radiations in several species falls temporally into the following periods: (1) initial, (2) acute, (3) subacute, and (4) chronic. The manifestations of each period differ somewhat according to species, and the periods should be distinguished by clinical course rather than by specific times. Direct evidence for temporal differences in clinical effects is provided by the observation that for a given dose rate, but different duration of exposure, e.g,. different total doses of single lethal exposure to total body x-irradiation, deaths occur in waves.